A viewshed is the geographical area that is visible from a location. It includes all surrounding points that are in line-of-sight with that location and excludes points that are beyond the

horizon The horizon is the apparent line that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This line divides all viewing directions based on whether i ...

or obstructed by terrain and other features (e.g., buildings, trees). Conversely, it can also refer to area from which an object can be seen. A viewshed is not necessarily "

visible Visibility, in meteorology, is a measure of the distance at which an object or light can be seen. Visibility may also refer to: * A measure of turbidity in water quality control * Interferometric visibility, which quantifies interference contrast ...

" to humans; the same concept is used in

radio communication Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmit ...

s to indicate where a specific combination of transmitter, antenna, and terrain allow reception of signal. Viewsheds are commonly used in

terrain analysis Geomorphometry, or geomorphometrics ( grc, γῆ, gê, earth + grc, μορφή, morphḗ, form, shape + grc, μέτρον, métron, measure), is the science and practice of measuring the characteristics of terrain, the shape of the surface of th ...

, which is of interest to

urban planning Urban planning, also known as town planning, city planning, regional planning, or rural planning, is a technical and political process that is focused on the development and design of land use and the built environment, including air, water, ...

archaeology Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landscap ...

, and

military science Military science is the study of military processes, institutions, and behavior, along with the study of warfare, and the theory and application of organized coercive force. It is mainly focused on theory, method, and practice of producing mil ...

. In urban planning, for example, viewsheds tend to be calculated for areas of particular scenic or historic value that are deemed worthy of preservation against development or other change. Viewsheds are often calculated for public areas — for example, from public roadways, public parks, or high-rise buildings. The preservation of viewsheds is frequently a goal in the designation of open space areas,

green belt A green belt is a policy and land-use zone designation used in land-use planning to retain areas of largely undeveloped, wild, or agricultural land surrounding or neighboring urban areas. Similar concepts are greenways or green wedges, which hav ...

s, and

community separator In urban planning in the United States, a community separator (or simply a separator) is a parcel of undeveloped land, sometimes in the form of open space, separating two or more urban areas under different municipal jurisdictions which has been de ...

Representation

A viewshed can be represented by

raster data upright=1, The Smiley, smiley face in the top left corner is a raster image. When enlarged, individual pixels appear as squares. Enlarging further, each pixel can be analyzed, with their colors constructed through combination of the values for ...

indicating the visibility of a viewpoint for or from an area of interest. In a binary representation, a cell (shown graphically as a

pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the smal ...

) with a value of 1 (or "true") indicates that the viewpoint is visible from that cell, while a value of 0 (false) indicates that the viewpoint is not visible. In certain disciplines, such as radio communications, "visibility" may be

probabilistic Probability is the branch of mathematics concerning numerical descriptions of how likely an Event (probability theory), event is to occur, or how likely it is that a proposition is true. The probability of an event is a number between 0 and ...

and therefore the viewshed may be represented with non-integer values. Viewsheds for multiple points, lines, or areas may have counts or fractional values for queries involving "how much" or "how many" (e.g., how much of a highway is visible?).

Viewshed and total-viewshed computation

A terrain can be represented using a regular grid of points called Digital Elevation Model (DEM). Where each point of the DEM is represented by its coordinates X, Y and its height Z. Viewshed calculation on a large DEM is costly from a computational point of view. This cost is much higher when calculating the viewshed for all the points of the DEM, also called total-viewshed. A faster algorithm for computing the total-viewshed of large DEMs was proposed on.

History

Clifford Tandy is credited with coining the term "viewshed" in 1967 by analogy to ''

watershed Watershed is a hydrological term, which has been adopted in other fields in a more or less figurative sense. It may refer to: Hydrology * Drainage divide, the line that separates neighbouring drainage basins * Drainage basin, called a "watershe ...

''. The lexicographer

Grant Barrett Grant Barrett (born 1970) is an American lexicographer, specializing in slang, jargon and new usage, and the author and compiler of language-related books and dictionaries. He is a co-host and co-producer of the American weekly, hour-long public ...

cites a use of the term from 1970 in the ''

Oakland Tribune The ''Oakland Tribune'' is a weekly newspaper published in Oakland, California, by the Bay Area News Group (BANG), a subsidiary of MediaNews Group. Founded in 1874, the ''Tribune'' rose to become an influential daily newspaper. With the declin ...

''.

Related concepts

Viewsheds are a specific type of

visibility graph In computational geometry and robot motion planning, a visibility graph is a graph of intervisible locations, typically for a set of points and obstacles in the Euclidean plane. Each node in the graph represents a point location, and each edge repr ...

Isovist A single isovist is the volume of space visible from a given point in space, together with a specification of the location of that point. It is a geometric concept coined by Clifford Tandy in 1967 and further refined by the architect Michael Bene ...

s are a closely related concept that is more common in the study of

architecture Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and constructing building ...

. Viewsheds and isovists are sometimes said to be equivalent, however others have found differences between them. It has been argued that isovists are more focused on representing space whereas viewsheds are about the visibility of features. Also, the problems they are used in have different scales. Planners use viewsheds where terrain heights come into play whereas architects do not typically take that into account with isovists. The area from which a structure can be seen may be called the " Zone of Visual Influence." This can be referred to as the viewshed as well, though. Total-viewshed map refers to the map, where each point represents the number of Km² visible at that point in the DEM. The 3D-viewshed of a point (X,Y) of the DEM consists of the visible space from that point.

Zone of visual influence

A ''zone of visual influence'' is the area from which a development or other structure is theoretically visible. It is usually represented as a map using color to indicate visibility. Zones of visual influence are used to identify the parts of a landscape that will be affected by a development. They are of particular use to

landscape architects A landscape architect is a person who is educated in the field of landscape architecture. The practice of landscape architecture includes: site analysis, site inventory, site planning, land planning, planting design, grading, storm water manageme ...

in determining visual intrusion as part of an

environmental impact assessment Environmental Impact assessment (EIA) is the assessment of the environmental consequences of a plan, policy, program, or actual projects prior to the decision to move forward with the proposed action. In this context, the term "environmental imp ...

. Zones of visual influence have been used extensively in

wind farm A wind farm or wind park, also called a wind power station or wind power plant, is a group of wind turbines in the same location used Wind power, to produce electricity. Wind farms vary in size from a small number of turbines to several hundre ...

development. A map will be created showing the number of

wind turbine A wind turbine is a device that converts the kinetic energy of wind into electrical energy. Hundreds of thousands of large turbines, in installations known as wind farms, now generate over 650 gigawatts of power, with 60 GW added each year. ...

s that are visible from a particular area. A cumulative zone of visual influence is used to define the cumulative effects of many developments. Zones of visual influence are created using

GIS A geographic information system (GIS) is a type of database containing Geographic data and information, geographic data (that is, descriptions of phenomena for which location is relevant), combined with Geographic information system software, sof ...

tools.

References

{{Reflist, refs= {{cite book , title=Visual Impact Assessment for Highway Projects , date=September 1990 , url=http://www.dot.ca.gov/ser/downloads/visual/FHWAVisualImpactAssmt.pdf , publisher=U.S. Department of Transportation, Federal Highway Administration, Office of Environmental Policy , location=Washington, DC , pages=26–33, 123 Publication number FHWA-HI-88-054. {{cite journal , title=Exploring the Visual Landscape - Introduction , journal=Research in Urbanism Series , volume=2 , first1=Steffen , last1=Nijhuis , first2=Ron , last2=van Lammeren , first3=Marc , last3=Antrop , url=http://rius.tudelft.nl/index.php/rius/article/view/205 , page=30 , date=September 2011 , doi=10.7480/rius.2.205 {{cite journal , title=From isovists to visibility graphs: a methodology for the analysis of architectural space , last1=Turner , first1=A , last2=Doxa , first2=M , last3=O'Sullivan , first3=D , last4=Penn , first4=A , journal=Environment and Planning B: Planning and Design , volume=28 , issue=1 , pages=103–121 , year=2001 , url=http://www.envplan.com/abstract.cgi?id=b2684 , doi=10.1068/b2684 , s2cid=17332950 {{cite journal , title=Mapping landscape openness with isovists , first=Gerd , last=Weitkamp , journal=Research in Urbanism Series , volume=2 , page=208 , date=September 2011 , issn=1879-8217 , url=http://rius.tudelft.nl/article/view/213/268 , doi=10.7480/rius.2.213 {{cite journal , title=Efficient data structure and highly scalable algorithm for total-viewshed computation , last1=Tabik , first1=S , last2=Cervilla , first2=A , last3=Zapata , first3=E , last4=Romero, first4=F , journal=IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing , volume=8 , issue=1 , pages=304–310 , year=2015 , doi=10.1109/jstars.2014.2326252 , bibcode=2015IJSTA...8..304T , s2cid=23232474 {{cite journal , title=Total 3D‐viewshed Map: Quantifying the Visible Volume in Digital Elevation Models , last1=Cervilla , first1=A , last2=Tabik , first2=S , last3=Vías , first3=J , last4=Mérida, first4=M , last5=Romero, first5=F , journal=Transactions in GIS , volume=21 , issue=3 , pages=304–310 , year=2016 , doi=10.1111/tgis.12216 Topography techniques Urban studies and planning terminology Environmental impact assessment

Representation

Viewshed and total-viewshed computation

History

Related concepts

Zone of visual influence

See also

References